Apparatus and method for plasma processing

ABSTRACT

At the time of plasma igniting or during plasma processing, only optimizing the distance between electrodes in each case caused a limitation to the prevention of charging damage. To resolve this, a novel plasma processing method employs a plasma processing apparatus which includes an upper electrode to which first high-frequency power is applied, a lower electrode to which second high-frequency power is applied, and a lift mechanism for controlling the spacing between the upper and lower electrodes. The first high-frequency power is applied to the upper electrode to cause plasma igniting. The method is adapted to make the spacing between the upper and lower electrodes larger at least at the time of plasma extinction than during plasma processing of a wafer on the lower electrode.

This application is a divisional of application Ser. No. 10/796,116,filed on Mar. 10, 2004, which claims priority to Japanese applicationno. 2003/063011, filed on Mar. 10, 2003. The entire contents ofapplication Ser. No. 10/796,116 are hereby incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for plasmaprocessing and more particularly to an apparatus and a method for plasmaprocessing which can reduce charging damage to objects to be processedbeing plasma processed using the plasma processing apparatus such as aparallel plate plasma processing apparatus.

2. Description of the Related Art

For example, conventionally known techniques of this type are disclosedin Japanese Patent Laid-Open Publication No. Hei 7-201496 (Claims 3 and9, and Paragraphs [0010], [0031], and [0037]), Japanese Patent Laid-OpenPublication No. Sho 61-265820 (Claim 1, Lines 6 to 13 on the top rightcolumn on page 2, Line 5 on the top left column on page 3 to line 2 onthe bottom left column on the same page, and the column stating theEffects of the Invention), and Japanese Patent No. 3113786 (Claims 1 and2, and Paragraphs [0029] and [0030]) (hereinafter, referred to asreferences 1 to 3, respectively).

The reference 1 suggests an apparatus and a method for generatingplasma. This apparatus includes a voltage application electrode forbeing applied high-frequency power, a ground electrode, and a distanceadjusting mechanism for variably adjusting the distance between theseelectrodes. When a voltage is applied to the voltage applicationelectrode, the distance between the voltage application electrode andthe ground electrode is reduced to such an extent as to readily providean igniting in accordance with the Paschen's law. After plasma has beenproduced, the distance between these electrodes is then increased,thereby ensuring a high etching capability and low damage to theprocessed body at the same time.

On the other hand, since the distance control mechanism for adjustingthe distance between the upper and lower electrodes makes the apparatuscomplicated, the reference 2 suggests a plasma processing apparatus thatrequires no distance control mechanism. This plasma processing apparatushas two electrodes, which are isolated from each other and eachconnected with an individual high-frequency power supply, and thedistances between these electrodes and a ground electrode disposed toface these electrodes are different. With this apparatus, thehigh-frequency power applied to an electrode spaced apart farther fromthe ground electrode is stopped immediately after a discharge isinitiated, thereby allowing for readily initiating a discharge at a lowvoltage even for high-rate etching. In other words, different electrodesare used for plasma igniting and plasma processing.

On the other hand, the reference 3 suggests a plasma processingapparatus with a two-frequency application scheme to apply respectivehigh-frequency powers to the upper and lower electrodes. With thisapparatus, the ON or OFF timing of the high-frequency powers applied toboth the upper and lower electrodes is controlled to alleviate chargingdamage.

However, in the conventional plasma processing methods as suggested inthe references 1 and 2, the distance between the upper and lowerelectrodes was optimized each at the time of plasma igniting and duringplasma processing to alleviate charging damage and optimize the plasmaprocessing at the same time. However, significant progress was madesince then toward finer-line and thinner-film processes forsemiconductor devices followed by significant improvements in plasmaprocessing apparatuses. This resulted in only the distance between theelectrodes being optimized each at the time of plasma igniting andduring plasma processing, yet causing a limitation to the prevention ofcharging damage.

The present invention was developed to solve the aforementioned problem.It is therefore an object of the invention to provide an apparatus and amethod for plasma processing which can prevent charging damage toobjects to be processed even when progress will be made towardfiner-line and thinner-film processes for semiconductor devices.

SUMMARY OF THE INVENTION

A plasma processing method according to a first aspect of the presentinvention is characterized in that when plasma processing an object tobe processed using a plasma processing apparatus for allowing plasmagenerating means to cause plasma igniting, an amount of chargesdeposited on the object to be processed at least at the time of plasmaextinction is reduced.

A plasma processing method according to a second aspect of the presentinvention employs a plasma processing apparatus which has an upperelectrode and a lower electrode, a spacing therebetween beingadjustable, and which causes plasma igniting by applying high-frequencypower to at least one of the upper and lower electrodes. The method ischaracterized in that when plasma processing an object to be processedplaced on the lower electrode using the plasma processing apparatus, thespacing is made larger at least at the time of plasma extinction thanduring plasma processing.

The plasma processing method according to a third aspect of the presentinvention, based on the second aspect of the invention, is characterizedin that first high-frequency power is applied to the upper electrode,while second high-frequency power having a lower frequency than thefirst high-frequency power is applied to the lower electrode.

The plasma processing method according to a fourth aspect of the presentinvention, based on the second or third aspect of the invention, ischaracterized in that to increase the spacing, the lower electrode ismoved away from the upper electrode.

The plasma processing method according to a fifth aspect of the presentinvention, based on the third or fourth aspect of the invention, ischaracterized in that the first high-frequency power is turned off afterthe second high-frequency power is turned off.

The plasma processing method according to a sixth aspect of the presentinvention, based on any one of the first to fifth aspects of theinvention, is characterized by performing etching as the plasmaprocessing.

A plasma processing apparatus according to a seventh aspect of thepresent invention includes a lower electrode for placing an object to beprocessed thereon, an upper electrode disposed above the lower electrodeso as to oppose it, an adjusting mechanism for adjusting a spacingbetween the upper and lower electrodes by raising or lowering the lowerelectrode, and a high-frequency power supply for applying high-frequencypower to at least one of the upper and lower electrodes, in which thehigh-frequency power is applied to either one of the electrodes to causeplasma igniting. The plasma processing apparatus is characterized inthat the adjusting mechanism has a drive mechanism for making thespacing larger at least at the time of plasma extinction than duringplasma processing of an object to be processed placed on the lowerelectrode.

The plasma processing apparatus according to an eighth aspect of thepresent invention, based on the seventh aspect of the invention, ischaracterized by including a first high-frequency power supply forapplying first high-frequency power to the upper electrode, and a secondhigh-frequency power supply for applying second high-frequency powerhaving a lower frequency than the first high-frequency power to thelower electrode.

The plasma processing apparatus according to a ninth aspect of thepresent invention, based on the seventh or eighth aspect of theinvention, is characterized in that the adjusting mechanism has a drivemechanism for moving the lower electrode away from the upper electrode.

The plasma processing apparatus according to a tenth aspect of thepresent invention, based on the eighth or ninth aspect of the invention,is characterized in that the first high-frequency power is turned offafter the second high-frequency power is turned off.

The plasma processing apparatus according to an eleventh aspect of thepresent invention, based on any one of the seventh to tenth aspects ofthe invention, is characterized by performing etching as the plasmaprocessing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating the structure of a plasmaprocessing apparatus according to an embodiment, which is employed for aplasma processing method of the present invention;

FIGS. 2A to 2C are explanatory views illustrating how the lowerelectrode works during a step of plasma processing in the plasmaprocessing apparatus shown in FIG. 1, FIG. 2A being a sectional viewillustrating the upper and lower electrodes being spaced apart fartherat the time of plasma igniting than the optimum spacing provided duringplasma processing, FIG. 2B being a sectional view illustrating the upperand lower electrodes being set to the optimal spacing provided duringplasma processing, FIG. 2C being a sectional view illustrating the upperand lower electrodes being spaced apart farther at the time of plasmaextinction than the optimum spacing provided during plasma processing;

FIG. 3 is an explanatory view illustrating the timing of application anddisconnection of first and second high-frequency powers;

FIG. 4 is an explanatory view illustrating the timing of application anddisconnection of the first and second high-frequency powers;

FIG. 5 is a schematic plan view illustrating a defective wafer that hasbeen processed by a conventional plasma processing method in which theupper and lower electrodes are set at an optimum spacing;

FIGS. 6A and 6B are schematic sectional views illustrating the CHARM®-2wafer sensor, FIG. 6A showing a potential sensor, FIG. 6B showing acurrent sensor; and

FIG. 7 is a graph showing the relation between the wafer process timeand the amount of charges supplied onto each device of a wafer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors decided to thoroughly address the present charging damage.To this end, for example, a parallel plate plasma processing apparatuswith the two-frequency application scheme was used for applyinghigh-frequency powers to the upper and lower electrodes at differentfrequencies, respectively. With this apparatus, the distance between theupper and lower electrodes was optimized. Under this condition, plasmaigniting, plasma processing (etching), and plasma extinction areperformed on a wafer to determine the distribution of breakdown voltagesof an antenna MOS (with an antenna ratio of one million). Consequently,as shown by the shaded lines illustrated in FIG. 5, defective devicesdue to a breakdown in the gate insulating film were found at the centralportion and periphery of the wafer, resulting in up to a yield of 45%.

In this regard, the inventors employed CHARM®-2 wafer (Wafer ChargingMonitors, Inc.) for monitoring charging of wafer to determine thepercentage of defective devices resulting from charging damage to eachdevice. As shown in FIGS. 6A and 6B, the CHARM®-2 wafer includes apotential sensor (see FIG. 6A), a current sensor (see FIG. 6B), and a UVsensor. Each sensor has a CCE (Charging Collection Electrode) on itssurface and an EEPROM serving as the storage portion of each sensor thatis initially set to a predetermined potential. As a result, thepotential sensor showed that the periphery of the wafer was positivelycharged while the central portion was negatively charged. Additionally,the current sensor showed that a positive current flew through theperiphery of the wafer, while a negative current flew through thecentral portion, thereby causing the breakdown of the gate insulatingfilm to occur in the periphery and the central portion of the wafer.

Further examined was the relation between the spacing between the upperand lower electrodes and the charging using the CHARM®-2 wafer. Thisexamination showed that charging damage was reduced with increasingspacing between the upper and lower electrodes. However, there is atradeoff between the spacing between the upper and lower electrodesbeing increased and the process performance (e.g., uniformity, etchingrate, and etched features). Thus, only an increase in the spacingbetween the electrodes provides no compatibility between the chargingdamage and the process performance.

In this regard, with the distance between the upper and lower electrodesbeing set to an optimum value, a wafer having MOS devices was plasmaprocessed to determine the relation between the duration of waferprocessing and the amount of charges (electric current) supplied fromthe plasma to the MOS device. As a result, the relation was found to beexpressed by the model indicated by the alternate long and short dashedlines shown in FIG. 7. In this figure, the current from point A to D canbe integrated with respect to time to obtain the amount of charging ofthe device. In FIG. 7, point A indicates the time of application ofhigh-frequency power, point B indicating the time of igniting, point Cindicating the time of plasma extinction resulting from thehigh-frequency power being ceased, point D indicating the time of theplasma processing being terminated, and the interval between points Band C indicating the duration of plasma processing.

As can be seen from FIG. 7, there is a fairly large amount of chargingnot only during the period from the time of high-frequency application(point A) to time of the plasma igniting (point B) but also during theperiod from the time of plasma extinction (point C) to the time ofplasma processing being terminated (point D). It was thus found thatsuch charging greatly contributed to charging damage. Based on thisfact, the currents present during the period from the time ofhigh-frequency application (point A) to the time of plasma igniting(point B) and during the period from the time of plasma extinction(point C) to the time of plasma processing being terminated (point D)were attempted to be reduced from the alternate long and short dashedlines to the real lines as shown by the arrows in the figure in order toreduce the total amount of charging. By this, it was found that animbalance between the amounts of positive and negative charges withinthe wafer surface was reduced, thus preventing or significantlyalleviating charging damage such as breakdown in the gate insulatingfilm.

Now, the present invention will be described below in more detail withreference to FIGS. 1 to 4 in accordance with the embodiments.

First, an example of a plasma processing apparatus used for a method ofthe present invention will be explained with reference to FIG. 1. Asshown in FIG. 1, by way of example, a plasma processing apparatus 10employed in this embodiment includes a chamber 11 made of a conductivematerial such as aluminum, an upper electrode 12 disposed on the uppersurface in the chamber 11, a lower electrode 13 for placing a wafer Wthereon, the lower electrode 13 being disposed below the upper electrode12 so as to oppose it, and a lift mechanism (e.g., an air cylinder) 14for adjusting the spacing between the lower electrode 13 and the upperelectrode 12 by raising or lowering the lower electrode 13.

The upper electrode 12, having a plurality of holes 12A formed on theentire lower surface thereof, serves as a showerhead for supplyingprocess gases. The center hole on the upper surface of the upperelectrode 12 is connected with a gas supply pipe 15, which is in turnconnected with a gas source 16 via a mass flow controller 17, to supplya process gas from the gas source 16 into the chamber 11 while the flowof the process gas is being controlled by the mass flow controller 17.The upper electrode 12 is also connected with a first high-frequencypower supply 18 via a matching device 19, allowing the firsthigh-frequency power supply 18 to apply first high-frequency power tothe upper electrode 12, e.g., at 13.56 to 150 MHz.

Inside the lower electrode 13, there is provided temperature controlmeans 20, such as a cooling jacket, which sets the wafer W held on thelower electrode 13 to the desired processing temperature. Thetemperature control means 20 has a supply pipe 21 and an exhaust pipe 22for circulating a coolant through the cooling jacket. This configurationallows the coolant controlled at a predetermined temperature to besupplied through the supply pipe 21 into the cooling jacket as well as aheat-exchanged coolant to be exhausted outwardly through the exhaustpipe 22. Additionally, the lower electrode 13 is connected with a secondhigh-frequency power supply 23 via another matching device 24, allowingthe second high-frequency power supply 23 to apply second high-frequencypower (bias) to the lower electrode 13, e.g., at 400 kHz to 13.56 MHz.Furthermore, the lower electrode 13 may also be provided therein with aheater or a Peltier device instead of the cooling jacket.

There is placed an electrostatic chuck 25 on the upper surface of thelower electrode 13. The electrostatic chuck 25 has a tungsten electrodeplate 25A interposed in between ceramic layers formed by sintering orspray forming. The tungsten electrode plate 25A is connected with avariable DC voltage source 26 via a filter 27 and a lead wire 28. Thevariable DC voltage source 26 applies a high DC voltage to the tungstenelectrode plate 25A, thereby causing the wafer W placed on the lowerelectrode 13 to be electrostatically attracted to the ceramic layers.

On the outer circumferential edge of the lower electrode 13, there isprovided an annular focus ring 29, which is adapted to surround thewafer W held electrostatically on the electrostatic chuck 25. The focusring 29, selectively made of an insulating or conductive materialdepending on the process, serves to confine or spread reactive ions.Also disposed between the chamber 11 and the lower electrode 13 is anexhaust ring 30 having a plurality of ventilating holes bored therein.The exhaust ring 30 is disposed at a level lower than the upper surfaceof the lower electrode 13 to surround the lower electrode 13. Thisexhaust ring 30 puts the exhaust flow into order and optimally confinesthe plasma in between the upper electrode 12 and the lower electrode 13.

Inside the lower electrode 13, there is also formed a flow path (notshown) for supplying therethrough a thermally conductive gas (e.g., Hegas) as a backside gas. The gas flow path, having a plurality ofopenings at the central portion and the peripheral edge of the wafer W,supplies the backside gas to between the electrostatic chuck 25 and thewafer W to enhance the thermal conductivity between the lower electrode13 and the wafer W, thereby making it possible to quickly control thewafer W at a predetermined temperature.

At a lower portion in the chamber 11, there is formed an exhaust portion11A connected to a vacuum exhaust apparatus (not shown), which creates avacuum in the chamber 11 and then allows the chamber 11 containing aprocess gas introduced therein to be maintained under a predetermineddegree of vacuum. The gas source 16 has a plurality of gas sources, eachof which supplies as an etchant gas, e.g., fluorocarbon-based gases suchas C₄F₈, a carbon monoxide (CO) gas, an oxygen (O₂) gas, or rare gasessuch as an argon (Ar) gas. Each gas is flow controlled by the mass flowcontroller 17 to be supplied at the desired flow rate.

Now, a plasma processing method that employs the plasma processingapparatus 10 will be explained with reference to FIGS. 2 and 3 inaccordance with an embodiment of the present invention. In thisembodiment, a 300 mm wafer W is etched.

For etching, the temperatures of the inner circumferential surface ofthe chamber 11, the upper electrode 12, and the lower electrode 13 arepre-set to 50° C., 30° C., and 10° C., respectively. Under thiscondition, as shown in FIG. 2A, the spacing between the upper electrode12 and the lower electrode 13 in the chamber 11 is first set to aspacing (e.g., 22 mm) greater than the optimum spacing (e.g., 17 mm)employed for etching the wafer W. Then, a gate valve (not shown) isopened to place the wafer W on the lower electrode 13 in the chamber 11,and the gate valve is then closed. Subsequently, C₄F₈, CO, Ar, and O₂gases are introduced as an etchant gas from the gas source 16 into thechamber 11 at a predetermined flow rate (e.g.,C₄F₈:CO:Ar:O₂=20:40:550:12 (sccm)), so that the chamber 11 is set to apressure of 40 mTorr.

Meanwhile, the variable DC voltage source 26 applies a high DC voltageto the tungsten electrode plate 25A in order to securely attract thewafer W to the lower electrode 13 in an electrostatic manner. A backsidegas (e.g., He gas) is supplied as well. At this time, the backside gasis set to pressures of 12 Torr at the central portion of the wafer W aswell as to 20 Torr at the circumferential edge of the wafer W. Thetemperature control means 20 in the lower electrode 13 maintains thewafer W at the predetermined temperature.

Now, as shown by {circle around (1)} in FIG. 3, by way of example, 15seconds after the application of the high DC voltage, the firsthigh-frequency power supply 18 applies the first high-frequency power of2000 W to the upper electrode 12 at 27 MHz to cause a glow dischargebetween the upper electrode 12 and the lower electrode 13 for plasmaigniting. As shown by {circle around (2)} in FIG. 3, two seconds afterthe application of the first high-frequency power, the secondhigh-frequency power supply 23 applies the second high-frequency powerof 1400 W to the lower electrode 13 at 800 kHz, thereby generating abias potential on the lower electrode 13. At this time, the timing ofapplying the second high-frequency power to the lower electrode 13 isdelayed by about 0.2 to 3 seconds with respect to the timing of applyingthe first high-frequency power to the upper electrode 12, therebyallowing the matching device 24 to provide a smooth matching to thesecond high-frequency power. Similarly, for the application of the firstand second high-frequency power to the lower electrode, the secondhigh-frequency power is delayed, thereby allowing the matching device toprovide a smooth matching.

As shown by {circle around (3)} in FIG. 3, at the point in timeimmediately thereafter, the lift mechanism 14 is actuated to raise thelower electrode 13. As shown in FIG. 2B, the lift mechanism 14 thenstops when the spacing between the lower electrode 13 and the upperelectrode 12 has reached the optimum spacing of 17 mm. Under thiscondition, the first and second high-frequency powers are stabilized at2000 W and 1400 W, respectively, to etch the wafer W.

As shown by {circle around (4)} in FIG. 3, at the point in timeimmediately before turning off the first high-frequency power supply 18following the etching having been performed for a predeterminedduration, the lift mechanism 14 is actuated to lower the lower electrode13. Then, as shown in FIG. 2C, the spacing between the upper electrode12 and the lower electrode 13 is increased to reach 22 mm to provide alarger spacing to between the upper and lower electrodes 12, 13,allowing the lift mechanism 14 to stop. Now, as shown by {circle around(1)} and {circle around (2)} in FIG. 3, the first high-frequency powersupply 18 is turned off, and the second high-frequency power supply 23is turned off 0.1 seconds thereafter to cause plasma extinction, therebyterminating the etching. Subsequently, 20 seconds after the etching hasbeen terminated, the variable DC voltage source 26 is turned off torelease the electrostatic attraction of the wafer W provided by theelectrostatic chuck 25. The wafer W is then taken out of the chamber 11.No defective devices caused by charging damage were found in this waferW resulting in a yield of 100%.

As a comparative example for comparison with this embodiment, a wafer Wwas etched in the same manner as the aforementioned embodiment exceptthat the plasma extinction was provided while the spacing between theupper electrode 12 and the lower electrode 13 was held at the optimumvalue of 17 mm without lowering the lower electrode 13. As a result, theyield of the devices slightly decreased to 99%. On the other hand, awafer W was etched in the same manner as the aforementioned embodimentexcept that the spacing between the upper electrode 12 and the lowerelectrode 13 was set at the optimum value of 17 mm with the lowerelectrode 13 being fixed throughout the etching. This resulted in ayield of only 77%.

As shown in FIG. 4, plasma extinction is provided through a step-downsequence in which the first high-frequency power supply 18 is turned offin two stages to prevent particles from adhering to the wafer W whenetched. Now, the present invention will be described in accordance withan embodiment incorporating the step-down sequence.

In this embodiment, the plasma igniting and the plasma processing arecarried out in the same manner as in the aforementioned embodimentexcept that the plasma extinction is carried out through the step-downsequence. That is, by way of example, to provide plasma extinctionthrough the use of the step-down sequence, the spacing between the upperelectrode 12 and the lower electrode 13 is increased from the optimumspacing of 17 mm to 25 mm. Then, as shown in FIG. 4, the firsthigh-frequency power is decreased from 2000 W to 200 W, and the secondhigh-frequency power is turned off 0.1 seconds thereafter. When thefirst high-frequency power is decreased to 200 W, the flow of the Ar gasin the etchant gas is decreased from 550 sccm to 500 sccm, while thepressure of the chamber 11 is increased from 40 mTorr to 200 mTorr.Under this condition, the wafer W is processed for 21 seconds.Thereafter, the first high-frequency power is completely turned off toprovide plasma extinction. The processes following the plasma extinctionare the same as those of the aforementioned embodiment. The wafer Wprocessed through the step-down sequence provides a yield of 100% to thedevices without any defective devices caused by charging damage. In theforegoing, the timings {circle around (1)} to {circle around (4)} shownin FIG. 4 correspond to the timings {circle around (1)} to {circlearound (4)} shown in FIG. 3, respectively.

To compare with this embodiment, the first high-frequency power wasturned off through two stages (2000 W→200 W→0 W) in accordance with thestep-down sequence to provide plasma extinction while the spacingbetween the upper electrode 12 and the lower electrode 13 was being heldat the optimum value of 17 mm without increasing the spacing at the timeof plasma extinction. In this case, defective devices due to chargingdamage were found, causing a decrease in their yield down to 44%. Thisshowed that the use of the step-down sequence does not provide asufficient prevention of charging damage only by increasing the spacingbetween the upper and lower electrodes 12, 13 at the time of plasmaigniting.

As described above, according to this embodiment, when a wafer W isplasma processed using the plasma processing apparatus 10, the lowerelectrode 13 is lowered, during the plasma igniting (the time from pointA to point B in FIG. 7) and the plasma extinction (the time from point Cto point D in FIG. 7), thereby causing the spacing between the upperelectrode 12 and the lower electrode 13 to become larger than theoptimum distance therebetween provided during the plasma processing (thetime from point B to point C in FIG. 7). This makes it possible toreduce the amount of charges deposited on the wafer W during the plasmaigniting and the plasma extinction, thereby preventing charging damageto the wafer W.

Furthermore, according to this embodiment, the first high-frequencypower is turned off after the second high-frequency power is turned off.This ensures particularly that the plasma extinction is carried outsmoothly to reduce charges to be deposited on the wafer W and particlesare prevented from adhering to the wafer W.

In the aforementioned embodiment, a plasma processing method has beendescribed in which the plasma processing apparatus 10 employing thetwo-frequency application scheme is used to separately apply the firstand second high-frequency powers to the upper and lower electrodes 12,13 for etching; however, the present invention is not limited thereto.For example, the method of the present invention can also employs aplasma processing apparatus for applying high-frequency power to one ofthe upper and lower electrodes to generate plasma or a plasma processingapparatus of an ECR (with a magnetic field) type. Furthermore, theplasma processing method of the present invention can also employ aplasma processing apparatus including other plasma generating means.Still furthermore, the plasma processing method of the present inventioncan be applied to plasma processing other than etching, such as CVD. Inessence, the present invention is intended to reduce the amount ofcharges deposited on an object to be processed at least during plasmaextinction when a plasma processing apparatus employing plasmagenerating means to provide plasma igniting is used for plasmaprocessing of the object to be processed.

Even when progress is made toward finer-line and thinner-film processesfor semiconductor devices, according to the first to eleventh aspects ofthe invention, provided are a plasma processing apparatus and a methodfor plasma processing which can prevent charging damage to objects to beprocessed by reducing the amount of charges deposited thereon duringplasma processing and preventing an imbalance between the amounts ofpositive and negative charges on the surface thereof.

What is claimed is:
 1. A plasma processing method comprising: providinga lower electrode for placing an object to be processed thereon;providing an upper electrode disposed above the lower electrode andopposing the lower electrode; providing an adjusting mechanism thatadjusts a spacing between the upper and lower electrodes by raising orlowering the lower electrode, the adjusting mechanism including a drivemechanism; providing a variable DC voltage source that applies DCvoltage to the lower electrode; providing a first high-frequency powersupply that applies first high-frequency power to the upper electrode,the first high-frequency power being applied to the upper electrode tocause plasma ignition; providing a second high-frequency power supplythat applies second high-frequency power to the lower electrode;applying the DC voltage to the lower electrode; applying a first valueof the first high-frequency power to the upper electrode; applying asecond value of the second high-frequency power to the lower electrode;minimizing an amount of charge on devices on the object for an ignitingduration by maintaining the spacing during the igniting period at aconstant second spacing, which is larger than a constant first spacing,for an initial period of time immediately after the time of plasmaignition; subsequently setting the spacing from the constant secondspacing directly to the constant first spacing; minimizing the amount ofcharge on devices on the object for an extinction duration bysubsequently setting the spacing from the constant first spacingdirectly to the constant second spacing, before the time of plasmaextinction; subsequently decreasing the first high-frequency power fromthe first value of the first high-frequency power to a third value ofthe first high-frequency power, decreasing a flow of processing gas,increasing pressure of a chamber, turning off the second high-frequencypower from the second value of the second high-frequency power, andturning off the first high-frequency power from the third value of thefirst high-frequency power; and subsequently turning off the variable DCvoltage source.
 2. The plasma processing method according to claim 1,further comprising moving the lower electrode away from the upperelectrode via the drive mechanism in the adjusting mechanism.
 3. Theplasma processing method according to claim 1, wherein etching isperformed as the plasma processing.
 4. The plasma processing methodaccording to claim 1, wherein the driving mechanism sets the spacing tothe first spacing after the time of plasma ignition.
 5. The plasmaprocessing method according to claim 1, wherein the first spacing is anarrowest spacing provided by the apparatus between the time of theplasma ignition and the time of plasma extinction.
 6. The plasmaprocessing method according to claim 5, wherein the first spacing is 17mm.
 7. The plasma processing method according to claim 1, wherein thefirst high-frequency power is turned on before the second high-frequencypower is turned on.
 8. The plasma processing method according to claim1, wherein the decreasing flow of processing gas decreases the flow from550 sccm to 500 sccm while the pressure of the chamber increases from 40m Torr to 200 m Torr.
 9. The plasma processing method according to claim1, wherein the second high frequency power is turned off 0.1 secondsafter the first high frequency is decreased to the third value.